1. Field of the Invention
The present invention relates to hollow cathode lamps used as light sources for atomic absorption spectrometry, atomic fluorescence spectrometry, and so on.
2. Related Background Art
In the atomic absorption spectrometry, it is necessary to use a light source for emitting an atomic spectral line of an analyte element itself, and hollow cathode lamps are known as such light sources. The hollow cathode lamps are configured to sputter the analyte element forming a hollow cathode by ion bombardment to scatter atoms of the analyte element in a discharge space and generate a spectral line through transfer of electron energy.
Meanwhile, as a problem arising during use of such hollow cathode lamps, there is the conventionally known phenomenon of self-absorption in which part of the spectral line imparts its energy to unexcited atoms of the element (unexcited element atoms) existing in the discharge space, thereby decreasing the intensity of the spectral line. If a rate of this self-absorption is high, optical output cannot be improved even with increase of an electric current supplied to the hollow cathode lamp.
Known techniques for solving the problem due to the self-absorption include, for example, the hollow cathode lamps described in U.S. Pat. Nos. 5,483,121 and 4,885,504. The hollow cathode lamps described in these publications both are provided with a thermoelectron supply (an auxiliary electrode for thermionic emission, electron emitter) for emitting thermoelectrons and are configured to excite the unexcited atoms by discharge with the thermionic emitter as a cathode. By exciting the unexcited atoms by the discharge with the thermionic emitter as a cathode in this way, it is feasible to prevent the absorption of the spectral line due to the unexcited atoms.
The hollow cathode lamps described in the above publications of U.S. Pat. Nos. 5,483,121 and 4,885,504, however, had the following problems. Namely, the element of the cathode is scattered by the aforementioned sputtering, this scattered element flies off with increase of the current supplied to the lamp over a certain level, the scattered element then scatters the spectral line, and the heavy scattering of the element results in deteriorating the effect of bringing the unexcited element into the excited state even by the discharge with the thermionic emitter as a cathode. This posed a problem that desired optical output was not gained even with increase in the working current of the lamp. There was another problem that the scattered element was heavily dispersed to adhere to the inner peripheral surface of a bulb of the lamp and thus become the cause of contamination of the bulb and it made preferred use thereafter difficult and made the lifetime of the lamp considerably shorter.
The present invention has been accomplished in view of the above circumstances and an object of the invention is to provide hollow cathode lamps that can provide high optical output and that is resistant to contamination on the internal surface of the bulb.
For accomplishing the above object, the present invention provides a hollow cathode lamp comprising, in a bulb having a light exit port, a hollow cathode and an anode opposed to the light exit port, the hollow cathode lamp comprising a tubular hood having a tubular shape, having one open end connected to the hollow cathode, having another open end opposed to the light exit port, and having an opening formed in a peripheral side face thereof; and an electron supply placed at a position to front on the opening, wherein discharge making use of thermoelectrons is implemented between the electron supply and the anode.
In the hollow cathode lamp according to the present invention, the cathode element scattered during the sputtering of the hollow cathode attaches onto the inner peripheral surface of the tubular hood and thus rarely contaminates the inner peripheral surface of the bulb. The tubular hood can prevent the situation of heavy dispersion of the scattered element in a wide area. This prevents the scattering of the spectral line emitted from the lamp, so as to improve the optical output. The opening is formed in the peripheral side face of the tubular hood and the electron supply for inducing the discharge making use of thermionic emission between the electron supply and the anode, in the hollow cathode and in the tubular hood is placed at the position to front on the opening. Then the discharge occurring through this opening between the electron supply and the anode can preliminarily excite the unexcited atoms existing in the hollow cathode and in the tubular hood, so as to prevent the self-absorption due to the unexcited atoms. At this time, since the tubular hood prevents the situation of heavy dispersion of the scattered element in a wide area, as described above, the foregoing discharge efficiently brings the unexcited element into the excited state.
The hollow cathode lamp according to the present invention is desirably configured to further comprise a cover covering the electron supply and the opening. When this configuration is adopted, it is feasible to prevent such a situation that the aforementioned cathode element scattered during the sputtering of the hollow cathode jumps out through the opening for supply of electrons, to deposit on the inner peripheral surface of the bulb.
A hollow cathode lamp according to another aspect of the present invention is a hollow cathode lamp comprising, in a bulb having a light exit port, a hollow cathode and an anode opposed to the light exit port, the hollow cathode lamp comprising a tubular hood having a tubular shape, having one open end connected to the hollow cathode, having another open end opposed to the light exit port, and having a slit formed in a peripheral side face thereof; and an electron supply placed at a position to front on the slit, wherein discharge making use of thermoelectrons is implemented between the electron supply and the anode.
In the hollow cathode lamp, the cathode element scattered during the sputtering of the hollow cathode attaches onto the inner peripheral surface of the tubular hood and thus rarely contaminates the inner peripheral surface of the bulb. The tubular hood can prevent the situation of heavy dispersion of the scattered element in a wide area. This prevents the scattering of the spectral line emitted from the lamp, so as to improve the optical output. The slit is formed in the peripheral side face of the tubular hood and the electron supply for inducing the discharge making use of the thermionic emission between the electron supply and the anode, in the hollow cathode and in the tubular hood is placed at the position to front on the slit. Then the discharge occurring through this slit between the electron supply and the anode can preliminarily excite the unexcited atoms existing in the hollow cathode, so as to prevent the self-absorption due to the unexcited atoms.
The hollow cathode lamp is desirably configured to further comprise a cover covering the electron supply and the slit. When this configuration is adopted, it is feasible to prevent such a situation that the aforementioned cathode element scattered during the sputtering of the hollow cathode jumps out through the slit for supply of electrons, to deposit on the inner peripheral surface of the bulb.
Further, in the hollow cathode lamps according to the present invention, desirably, the hollow cathode is a through cathode the interior of which is through, and the hollow cathode is located between the light exit port and the anode. When this configuration is adopted, because the anode is not located in the space between the hollow cathode and the light exit port, the existence of the anode does not impede traveling of light emitted from atoms when the atoms in the hollow cathode return into the ground state.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.